Dialysis machine having a conductivity sensor for determining fluid properties

ABSTRACT

This disclosure describes systems, devices and methods related to embodiments of a dialysis system, including a home dialysis system, having a conductivity sensor or sensing system that measures conductivity in fluid associated with the dialysis system. For example, the conductivity sensor of the dialysis system can measure the conductivity of dialysate in order to determine its composition and verify proportioning of the dialysate. The conductivity sensor can also measure the purity of water and verify its proportioning in the dialysis system. In addition, the conductivity sensor can be configured to detect conductivity of the fluid within an acceptable range.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Appin. No.62/052,410, filed Sep. 18, 2014, titled “Dialysis Machine Having aConductivity Sensor for Determining Fluid Properties”, which isincorporated herein by reference in its entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD

This disclosure is generally related to dialysis machines and therapy.This disclosure is more specifically related to conductivity sensors indialysis machines.

BACKGROUND

Some patients receive dialysis treatment at a dialysis center, which canplace a demanding, restrictive and tiring schedule on a patient.Patients who receive in-center dialysis may have to travel to thedialysis center at least three times a week and sit in a chair for 3 to4 hours each time while toxins and excess fluids are filtered from theirblood. After the treatment, the patient may be required to wait for theneedle site to stop bleeding and blood pressure to return to normal,which can require even more time taken away from other activities intheir daily lives. In contrast to dialysis center treatments, homedialysis can provide patients with scheduling flexibility as it permitspatients to choose treatment times.

SUMMARY OF THE DISCLOSURE

A conductivity sensor is provided, comprising a first pair of senseelectrodes having a first cell constant, a second pair of senseelectrodes having a second cell constant different than the first cellconstant, wherein the first and second pairs of sense electrodes areeach configured to measure a conductivity of a fluid, and wherein thefirst and second pairs of sense electrodes combine to increase a rangeof conductivity measurements that fall below an acceptable errorthreshold.

In some embodiments, the conductivity is disposed within a dialysissystem.

In one embodiment, the first cell constant ranges from 0.1 to 1.0. Inanother embodiment, the second cell constant ranges from 1.0 to 5.0.

In other embodiments, the first pair of sense electrodes comprises afirst sense electrode and a second sense electrode. In anotherembodiment, the second pair of sense electrodes comprises a third senseelectrode and a fourth sense electrode.

In some embodiments, the first and second sense electrodes arepositioned between a first drive electrode and a second drive electrode.In other embodiments, the third and fourth sense electrodes arepositioned between the second drive electrode and a third driveelectrode.

In one embodiment, the conductivity sensor further comprises a firstamplifier configured to measure voltages produced by the first andsecond pairs of sense electrodes. In another embodiment, theconductivity sensor further comprises a second amplifier configured tocombine the measured voltages from the first amplifier. In yet anotherembodiment, the conductivity sensor further comprises an attenuationelement configured to achieve scaled current subtraction with the secondamplifier.

A method of measuring a conductivity of a fluid is provided, comprisingthe steps of measuring a first voltage of the fluid with a first pair ofsense electrodes having a first cell constant, measuring a secondvoltage of the fluid with a second pair of sense electrodes having asecond cell constant different than the first cell constant, processingthe first and second voltages to produce first and second conductivityreadings, and combining the first and second voltages to produce acombined conductivity reading that falls below an acceptable errorthreshold.

In some embodiments, the processing step further comprises processingthe first and second voltages with a first amplifier to produce thefirst and second conductivity readings.

In another embodiment, the combining step further comprises combiningthe first and second voltages with a second amplifier to produce thecombined conductivity reading that falls below the acceptable errorthreshold.

In one embodiment, the first cell constant ranges from 0.1 to 1.0. Inanother embodiment, the second cell constant ranges from 1.0 to 5.0.

A dialysis system is provided, comprising a water purification systemconfigured to purify a water source for use with dialysis treatment, adialysis delivery system configured to produce a dialysate from waterpurified by the water purification system, and further configured toprovide dialysis treatment to a patient, and a conductivity sensordisposed in at least one of the water purification system and thedialysis delivery system, the conductivity sensor comprising a firstpair of sense electrodes having a first cell constant, and a second pairof sense electrodes having a second cell constant different than thefirst cell constant, wherein the first and second pairs of senseelectrodes are each configured to measure a conductivity of a fluid, andwherein the first and second pairs of sense electrodes combine toincrease a range of conductivity measurements that fall below anacceptable error threshold.

In one embodiment, the first cell constant ranges from 0.1 to 1.0. Inanother embodiment, the second cell constant ranges from 1.0 to 5.0.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe claims that follow. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates an example dialysis system that can provide dialysistreatment to a user in a non-clinical setting, such as in the user'shome.

FIG. 2 shows an embodiment of a conductivity sensor having a two-poleconfiguration that can be included in the dialysis system of FIG. 1.

FIG. 3 shows an example graph of a prospective error-to-conductivityrelationship of a conductivity sensor that has a single cell constant,such as the conductivity sensor shown in FIG. 2.

FIG. 4 shows another embodiment of a conductivity sensor that can beincluded in the dialysis system of FIG. 1 and includes a seven-electrodeconfiguration.

FIG. 5 shows an example graph that compares conductivity measurementsthat can be achieved by a conductivity sensor having a single cellconstant with conductivity measurements that can be achieved by aconductivity sensor having different cell constants, such as theconductivity sensor shown in FIG. 4.

FIG. 6 illustrates another embodiment of a conductivity sensor having aseven-electrode configuration and amplifiers for measuring voltageacross sense electrodes.

DETAILED DESCRIPTION

This disclosure describes a novel approach for investigating neuronalsignaling. The approach described herein exploits high dielectricpermittivity of biological tissue to tunnel energy to the implantabledevices in animals, that is, it uses tissue to facilitate the couplingof energy from the transmitter to the implanted receiver. Wherever theanimal is located, energy can be tunneled automatically to the implantedreceiver.

This disclosure describes systems, devices and methods related toembodiments of a dialysis system, including a home dialysis system,having a conductivity sensor or sensing system that measuresconductivity in fluid associated with the dialysis system. For example,the conductivity sensor of the dialysis system can measure theconductivity of dialysate in order to determine its composition andverify proportioning of the dialysate. The conductivity sensor can alsomeasure the purity of water and verify its proportioning in the dialysissystem. In addition, the conductivity sensor can be configured to detectconductivity of the fluid within an acceptable range, as will bedescribed in greater detail below.

The conductivity sensor can include drive electrodes (i.e., drivescurrent) and sense electrodes (i.e., measures voltage). The driveelectrodes can be powered by an alternating voltage, and current thatflows from the drive electrodes through the fluid can be measured by thesense electrodes to determine the conductivity of the fluid. Theconductivity of the fluid can be affected by one or more characteristicsof the fluid, such as chemical composition and temperature.

For example, the conductivity sensor can drive a current through thefluid and measure a drop in voltage across the fluid. Based on thecurrent, voltage, distance between sense electrodes and effective areabetween the sense electrodes, the conductivity sensor can calculate theconductivity across the fluid.

FIG. 1 illustrates an example dialysis system 100 that can providedialysis treatment to a user in a non-clinical setting, such as in theuser's home. The dialysis system 100 can include a water purificationsystem (WPS) module 102 and a dialysis delivery system (DDS) module 104that can be reversibly coupled together, such as for improved transportand storage. The WPS module 102 can assist in purifying a water sourcefor use with dialysis treatment. For example, the WPS module 102 can beconnected to a residential water source (e.g., tap water) and preparepasteurized water in at least near real-time. The pasteurized water canthen be used for dialysis (e.g., in the DDS module 104) in anon-clinical setting without the need to heat and cool large, batchedquantities of water. One or more conductivity sensors, including any ofthe conductivity sensors described herein can be included in thedialysis system 100 for measuring conductivity of a fluid associatedwith the dialysis system 100, such as dialysate or water.

FIG. 2 illustrates a conductivity sensor 200 having a two-poleconfiguration for use in a dialysis system. The conductivity sensor 200can include a positive drive/sense electrode 212 and a negativedrive/sense electrode 214. A current can be driven across the fluid 216(e.g., dialysate, water) between the drive/sense electrodes 212, 214 anda voltage drop can be measured between the drive/sense electrodes 212,214. The conductivity sensor 200 can calculate the conductivity of thefluid 216 based on the current, voltage, distance (d) between thedrive/sense electrodes 212, 214 and an effective area (A) between thedrive/sense electrodes 212, 214. For example, the distance and effectivearea between the drive/sense electrodes 212, 214 can be used tocalculate a cell constant, which can be used to calculate theconductivity. In addition, the variables of the cell constant (i.e., dand A) can be tuned so as to allow the conductivity sensor 200 tomeasure conductivity of the fluid 216 within an acceptable range (i.e.,relatively low measurement error).

FIG. 3 illustrates an example graph 300 of a prospectiveerror-to-conductivity relationship of a conductivity sensor, such asconductivity sensor 200, which has a single cell constant. As shown inthe graph 300, an acceptable range 322 can define conductivitymeasurements that can be achieved by the conductivity sensor that arebelow an acceptable error threshold 324. The acceptable range 322 can bebased on the cell constant of the conductivity sensor. As such, the cellconstant can be tuned (e.g., the d and/or A adjusted) in order toachieve a desired range of conductivity measurements that are within theacceptable range 322.

A number of variables in the dialysis system can interfere withconductivity measurements such that a more advanced conductivity sensoris needed. For example, electrical noise from other parts of thedialysis system and leakage currents can interfere with measuringconductivity of fluids within the dialysis system.

FIG. 4 illustrates an embodiment of a conductivity sensor 400 having aseven-electrode configuration that separates pairs of drive electrodesand sense electrodes. This configuration can provide several advantagesover other conductivity sensors, including conductivity sensor 200 ofFIG. 2, such as by shielding the conductivity sensor 400 from electricalnoise and variable ground paths.

As shown in FIG. 4, the conductivity sensor 400 can include a firstdrive electrode 430 a, a second drive electrode 430 b, and a third driveelectrode 430 c configured to drive current through a fluid 416 of thedialysis system. In addition, first and second sense electrodes 440 aand 440 b can be positioned between the first and second driveelectrodes 430 a and 430 b. Furthermore, third and fourth senseelectrodes 440 c and 440 d can be positioned between the second andthird drive electrodes 430 b and 430 c. In this configuration, each pairof sense electrodes (i.e., 440 a and 440 b, 440 c and 440 d) can have acell constant, which is defined as the ratio of the distance between theelectrodes to the electrode area. Furthermore, the first pair of senseelectrodes 440 a and 440 b can have a different cell constant than thesecond pair of sense electrodes 440 c and 440 d.

As described above, a cell constant is the ratio of the distance betweenelectrodes to the electrode area. The conductivity sensor 400 can havedistinct cell constants between the pairs of sense electrodes asfollows: For example, a first distance (d1) between the first and secondsense electrodes 440 a and 440 b can be different than a second distance(d2) between the third and fourth sense electrodes 440 c and 440 d.Alternatively or in addition, a first area (A1) of the first and secondsense electrodes 440 a and 440 b can be different than a second area(A2) of the third and fourth sense electrodes 440 c and 440 d. This canresult in the cell constant created by the first and second senseelectrodes 440 a and 440 b to be different than the cell constantcreated by the third and fourth sense electrodes 440 c and 440 d. Theconductivity sensor 400 includes two pairs of electrodes with differentcell constants, whereby the combination of these two different cellconstants allows the conductivity sensor 400 to measure a wider range ofconductivity measurements that are below an acceptable error threshold,as will be explained in greater detail below.

FIG. 5 shows an example graph 500 that shows conductivity measurementsthat can be achieved by a conductivity sensor, such as conductivitysensor 400, having different cell constants (i.e., first conductivityline 550 and second conductivity line 552). As can be seen in graph 500,the first conductivity line 550 has a first conductivity range 522 a,and the second conductivity line 552 has a second conductivity range 522b. The first and second conductivity ranges are combined to form anextended conductivity range 522 c that falls below the limit ofacceptable error for the conductivity sensor 400. When the twoconductivity lines are combined, the conductivity sensor has a largeracceptable range 522 c of conductivity measurements that can becollected below the acceptable error threshold 524 compared to thesmaller acceptable ranges 522 a and 522 b the individual cell constants.As such, the conductivity sensor 400 having different cell constants canmeasure a greater range of conductivity measurements that haveacceptable errors.

The embodiment illustrated in FIG. 5 shows a conductivity sensor havinga first cell constant of K=0.5 and a second cell constant of K=1.0. Asthe conductivity decreases (increasing resistance) a given current willproduce a larger voltage signal. At some point the signal becomes solarge that the amplifier circuit has reached its upper voltage limit.But a conductivity censor having a first cell constant that is half thesize of the second cell constant cuts the voltage signal in half,effectively doubling the lower range of the sensor. For example, if thepractical lower limit of a sensor with K=1.0 is 100 uS, then a sensorwith a K of 0.5 has a practical lower limit of 50 uS.

Cell constants in conductivity sensor 400 can be tuned by eitherchanging the distance or effective area between the pairs of senseelectrodes in order to adjust the acceptable conductivity measurementrange of the conductivity sensor 400. This can allow the conductivitysensor 400 to collect a broad range of conductivity measurements thatare appropriate for the type of fluid being measured, along with themeasurements being below the acceptable error threshold 524.

FIG. 6 illustrates another embodiment of a conductivity sensor 600having a seven-electrode configuration. For example, the conductivitysensor 600 includes first and second sense electrodes 640 a and 640 bpositioned between first and second drive electrodes 630 a and 630 b. Inaddition, the conductivity sensor 600 includes third and fourth senseelectrodes 640 c and 640 d positioned between the second drive electrode630 b and a third drive electrode 630 c. The cell constant of the firstand second sense electrodes 640 a and 640 b can be different from thecell constant of the third and fourth sense electrodes 640 c and 640 d.First amplifiers 660 can assist in independently measuring the voltagesensed by the pairs of sense electrodes (i.e., 640 a and 640 b, 640 cand 640 d). A second amplifier 680 can process and combine theindependently measured voltage readings, such as from the firstamplifiers 660. The resulting signal from the second amplifier, oraveraging amplifier 680, can be further processed to produce a singleconductivity reading. The measurement error of the conductivity sensor600 can be the combination of measurement errors associated with eachpair of sense electrodes. In addition, the seven-electrode configurationlimits alteration of the conductivity reading obtained by theconductivity sensor 600 by external effect, such as from noise current682 and leakage current 684. With different cell constants within theconductivity sensor, an additional attenuation element 685 can be usedto achieve effectively scaled current subtraction with the averagingamplifier 680.

In some embodiments, additional electronics (e.g., sensors) can beincluded in the conductivity sensor 600 in order to ensure properfunctioning. For example, conductivity sensor 600 can include a sensor670 for measuring current along a section of the electrical pathway inorder to ensure that the current is staying within a preferred range.The preferred range can be a single preset value or a dynamically tunedvalue that assists the conductivity sensor 600 with achieving preciseconductivity calculations (i.e., minimize individual and combinedmeasurement errors for voltage and current).

In addition, by independently measuring voltage across the pairs ofsense electrodes, the conductivity sensor 600 can allow the senseelectrodes to be placed in a variety of positions relative to each otherbetween corresponding drive electrodes. Additionally, increasing thedifference in cell constants in the conductivity sensor 600 can increasethe acceptable range. The noise level can be decreased by decreasing thedifference in cell constants.

A target conductivity range of water and dialysate, for example, can befrom approximately 0 uS/cm to 1,000 uS/cm and approximately 8,000 uS/cmto 20,000 uS/cm, respectively. In addition, target cell constants foreach pair of sense electrodes can be approximately 0.1 to 1.0 andapproximately 1.0 to 5.0.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of an invention that is claimed orof what may be claimed, but rather as descriptions of features specificto particular embodiments. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or a variation of a sub-combination.Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Only a few examples and implementations are disclosed.Variations, modifications and enhancements to the described examples andimplementations and other implementations may be made based on what isdisclosed.

As for additional details pertinent to the present invention, materialsand manufacturing techniques may be employed as within the level ofthose with skill in the relevant art. The same may hold true withrespect to method-based aspects of the invention in terms of additionalacts commonly or logically employed. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein. Likewise, reference to a singular item,includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe subject specification, but rather only by the plain meaning of theclaim terms employed.

What is claimed is:
 1. A conductivity sensor, comprising: a first pairof sense electrodes having a first cell constant; a second pair of senseelectrodes having a second cell constant different than the first cellconstant; wherein the first and second pairs of sense electrodes areeach configured to measure a conductivity of a fluid, and wherein thefirst and second pairs of sense electrodes combine to increase a rangeof conductivity measurements that fall below an acceptable errorthreshold.
 2. The conductivity sensor of claim 1, wherein theconductivity sensor is disposed within a dialysis system.
 3. Theconductivity sensor of claim 1, wherein the first cell constant rangesfrom 0.1 to 1.0.
 4. The conductivity sensor of claim 1, wherein thesecond cell constant ranges from 1.0 to 5.0.
 5. The conductivity sensorof claim 1, wherein the first pair of sense electrodes comprises a firstsense electrode and a second sense electrode.
 6. The conductivity sensorof claim 5, wherein the second pair of sense electrodes comprises athird sense electrode and a fourth sense electrode.
 7. The conductivitysensor of claim 6, wherein the first and second sense electrodes arepositioned between a first drive electrode and a second drive electrode.8. The conductivity sensor of claim 7, wherein the third and fourthsense electrodes are positioned between the second drive electrode and athird drive electrode.
 9. The conductivity sensor of claim 8, furthercomprising a first amplifier configured to measure voltages produced bythe first and second pairs of sense electrodes.
 10. The conductivitysensor of claim 9, further comprising a second amplifier configured tocombine the measured voltages from the first amplifier.
 11. Theconductivity sensor of claim 10, further comprising an attenuationelement configured to achieve scaled current subtraction with the secondamplifier.
 12. A method of measuring a conductivity of a fluid,comprising the steps of: measuring a first voltage of the fluid with afirst pair of sense electrodes having a first cell constant; measuring asecond voltage of the fluid with a second pair of sense electrodeshaving a second cell constant different than the first cell constant;processing the first and second voltages to produce first and secondconductivity readings; and combining the first and second voltages toproduce a combined conductivity reading that falls below an acceptableerror threshold.
 13. The method of claim 12, wherein the processing stepfurther comprises processing the first and second voltages with a firstamplifier to produce the first and second conductivity readings.
 14. Themethod of claim 13, wherein the combining step further comprisescombining the first and second voltages with a second amplifier toproduce the combined conductivity reading that falls below theacceptable error threshold.
 15. The method of claim 12, wherein thefirst cell constant ranges from 0.1 to 1.0.
 16. The method of claim 12,wherein the second cell constant ranges from 1.0 to 5.0.
 17. A dialysissystem, comprising: a water purification system configured to purify awater source for use with dialysis treatment; a dialysis delivery systemconfigured to produce a dialysate from water purified by the waterpurification system, and further configured to provide dialysistreatment to a patient; and a conductivity sensor disposed in at leastone of the water purification system and the dialysis delivery system,the conductivity sensor comprising a first pair of sense electrodeshaving a first cell constant, and a second pair of sense electrodeshaving a second cell constant different than the first cell constant,wherein the first and second pairs of sense electrodes are eachconfigured to measure a conductivity of a fluid, and wherein the firstand second pairs of sense electrodes combine to increase a range ofconductivity measurements that fall below an acceptable error threshold.18. The dialysis system of claim 17, wherein the first cell constantranges from 0.1 to 1.0.
 19. The dialysis system of claim 17, wherein thesecond cell constant ranges from 1.0 to 5.0.